Suspended floor insulation 1930's.

[DanielE]

HI guys, 

 

I have had many opinions regarding suspended floor insulation, as floor is absolutely freezing. 

 

I have had two chains of thought, - some have said I need these fancy and expensive products. Pls see link below:

 

1) Diagram 8, shows the layout, with further diagrams showing the system in much greater dealer.  There are also two videos there. This would cost be several thousand pounds to undertake, 

 

https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors?srsltid=AfmBOoo_yGx1VeqhQuO_LLhq6hRBLrEelw5Tze1IiF-jV8P_ZWWzolEG

 

 

 

 

2) The second option is below. 

 

But in short, it is just fitting,, a breathable membrane, and then installing the insulation. Would Rhino Vent, ultra breathable work, or would I require, a different brand ? 

 

Thank you in advance.

 

Video below is way 2 of doing it. 

 

All advice in advance appreciated!

 

Thanks

 

 

 

 

 

 

 

Edited February 17 by DanielE
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[Big Jimbo]

I have never done this, but I have seen No2 done. The problem on older properties is that the floorboards are quite ofter tongue and groove, and getting them up without breaking a lot of them is hard work.

Would you have room for 20mm pir on top of the boards, with 9mm ply on top of that ? 30mm loss in room height ?

I don't know what the difference in heat loss between 20mm PIR, or even 10mm PIR against the fluffy stuff laid between joists ?

[Big Jimbo]

I will probably get shot here, but my 12 year old Physics tells me that heat rises, and therefore whats above stopping heat loss, is more important than whats below. At my daughters, because I was going to be gluing down LVT, i simply when over the floorboards with 9mm ply making sure it was tight and left no gaps. Just doing that, seemed to make a big difference to how the floor felt underfoot, as opposed to the bare floorboards.

[Sparrowhawk]

Hi @DanielE, having made a start on this in a 1920s house this winter (and working on the basis that insulation is good, but airtightness is even better): draping a membrane works, and doing it plus glass fibre fill is cheaper than PIR, but PIR is a easier (so long as you're not aiming for perfection). PIR is also easier in odd shaped rooms, and avoids trying to fix the membrane onto an uneven wall / get it round the asbestos-containing DPM sticking out of the wall which can't be cut but is in the way.

 

My thread when I asked this question (has product names for what you can use for draping) 

 

Why do I caveat PIR with "as long as you're not aiming for perfection"? Cutting it to fit exactly between joists is impossible, especially old ones. So you end up with gaps at the edges, which you need to foam up (or use Gapotape to make a snug fit). I suck at foaming small gaps, and you still have a thermally weak spot... so you won't get a perfect finish. For me that's okay given the fabric of the house, it's better than what's before. I then stick airtightness tape over these because what I really want to stop is the cold air coming into the house.

[Sparrowhawk]

6 minutes ago, Big Jimbo said:

At my daughters, because I was going to be gluing down LVT, i simply when over the floorboards with 9mm ply making sure it was tight and left no gaps. Just doing that, seemed to make a big difference to how the floor felt underfoot, as opposed to the bare floorboards.

I'm doing something similar in our hallway, because there's the stairs, an understairs toilet and stud walls built on top of the floorboards. Having spent way too long trying to figure out how to lift the floor, the pragmatic outcome is to lay an airtightness membrane over the top of the existing floor (and lap it up the walls), and then lay a new floor over the floor like you've done.

 

In this house the membrane is needed, because the previous occupants did exactly what you did, but the cold air still whistled out at the edges and around the skirting boards

[marshian]

48 minutes ago, Big Jimbo said:

I will probably get shot here, but my 12 year old Physics tells me that heat rises, and therefore whats above stopping heat loss, is more important than whats below. At my daughters, because I was going to be gluing down LVT, i simply when over the floorboards with 9mm ply making sure it was tight and left no gaps. Just doing that, seemed to make a big difference to how the floor felt underfoot, as opposed to the bare floorboards.

3 years ago I would have agreed with you and said insulating under the floor was a lot of work for little gain

 

I was very wrong - in my house it made a massive difference and along with a few other improvements halved my energy usage for space heating

[IGP]

I did the Ecological Building systems approach in my 30’s semi detached, and it’s made the world of difference. 
 

No draughts anywhere, and a warm floor in winter. Highly recommend. 

[thetdog666]

11 hours ago, marshian said:

3 years ago I would have agreed with you and said insulating under the floor was a lot of work for little gain

 

I was very wrong - in my house it made a massive difference and along with a few other improvements halved my energy usage for space heating

how much of a difference in temp did it make?

[thetdog666]

10 hours ago, IGP said:

I did the Ecological Building systems approach in my 30’s semi detached, and it’s made the world of difference. 
 

How much of a temperature difference did it make?

 

[marshian]

10 minutes ago, thetdog666 said:

how much of a difference in temp did it make?

 

None - we still heated to the same temp - just got there quicker on scheduled heating slots and didn't drop off a cliff as soon as the heating went off.

 

Looking at data from before insulation at similar OAT (around zero Deg C)

 

All the main ground floor rooms we would lose about 0.7 to 0.5 deg C per hour

 

After insulation around 0.25 to 0.20 deg C per hour

 

So taking one room as an example heating went off at 10pm at 20 Deg C room temp you could pretty much expect it to be around 13 deg at 8am next morning

 

After insulation you could expect it to be around 18 deg C

 

Takes a lot less energy and time to get a room from 18 to 20 than it does from 13 to 20

 

[thetdog666]

9 minutes ago, marshian said:

 

None - we still heated to the same temp - just got there quicker on scheduled heating slots and didn't drop off a cliff as soon as the heating went off.

 

Looking at data from before insulation at similar OAT (around zero Deg C)

 

All the main ground floor rooms we would lose about 0.7 to 0.5 deg C per hour

 

After insulation around 0.25 to 0.20 deg C per hour

 

So taking one room as an example heating went off at 10pm at 20 Deg C room temp you could pretty much expect it to be around 13 deg at 8am next morning

 

After insulation you could expect it to be around 18 deg C

 

Takes a lot less energy and time to get a room from 18 to 20 than it does from 13 to 20

 

massive improvement in comfort. Im putting a breathable membrane down with 140mm and 90mm (max depth possible with pipes etc) frametherm insulation. Still not decided if il put a vapour barrier down though

[marshian]

1 minute ago, thetdog666 said:

massive improvement in comfort. Im putting a breathable membrane down with 140mm and 90mm (max depth possible with pipes etc) frametherm insulation. Still not decided if il put a vapour barrier down though

 

Actually yes comfort was the biggest benefit - to a point where Mrs Alien wasn't happy if the living room was below 21 and I was happy with anything above 18

 

Now it's 19.5 to 20.5 and she's happy with room comfort (this means she can find something else to whine about which is not so great!)

[thetdog666]

2 minutes ago, marshian said:

 

Actually yes comfort was the biggest benefit - to a point where Mrs Alien wasn't happy if the living room was below 21 and I was happy with anything above 18

 

Now it's 19.5 to 20.5 and she's happy with room comfort (this means she can find something else to whine about which is not so great!)

typical women.....never happy haha

[thetdog666]

4 minutes ago, marshian said:

 

Actually yes comfort was the biggest benefit - to a point where Mrs Alien wasn't happy if the living room was below 21 and I was happy with anything above 18

 

Now it's 19.5 to 20.5 and she's happy with room comfort (this means she can find something else to whine about which is not so great!)

Was your floor as per Ecological Building system? What thickness of wool was used?

[marshian]

1 minute ago, thetdog666 said:

Was your floor as per Ecological Building system? What thickness of wool was used?

 

75mm PIR

 

I had to do it from under the floor due to tiled surfaces and 25mm oak planks

[marshian]

Pictures of what I did and where I was working in this thread if it helps any

 

 

[IGP]

It didn’t make a difference to the air temperature as that set to a steady 20c, but the floor itself was like 12c prior to insulation and now is about 19c post. Can happily walk on the floor barefoot and not be cold at all. 
 

We’ve got about 180mm of mineral wool for the insulation layer. 
 

Definitely put a vapour membrane on the top and tape to wall, stops moisture from the room air condensing inside the insulation layer. Do it once, do it right. 

[thetdog666]

4 hours ago, marshian said:

Pictures of what I did and where I was working in this thread if it helps any

 

 

I was going to use PIR but my joists are 350mm wide and the amount of pipes and cables underneath would of made it impossible to get a good finish

[thetdog666]

4 hours ago, IGP said:

It didn’t make a difference to the air temperature as that set to a steady 20c, but the floor itself was like 12c prior to insulation and now is about 19c post. Can happily walk on the floor barefoot and not be cold at all. 
 

We’ve got about 180mm of mineral wool for the insulation layer. 
 

Definitely put a vapour membrane on the top and tape to wall, stops moisture from the room air condensing inside the insulation layer. Do it once, do it right. 

Ace massive difference.  My joists are 120mm deep so only going to manage 90mm in certain places and 140mm in the rest due to pipework

 

Will do